TPU (thermoplastic polyurethane) polymers are typically made by reacting (1) a hydroxyl terminated polyether or hydroxyl terminated polyester, (2) a chain extender, and (3) an isocyanate compound. Various types of compounds for each of the three reactants are disclosed in the literature. The TPU polymers made from these three reactants find use in various fields where products are made by melt processing the TPU and forming it into various shapes to produce desired articles by processes such as extrusion and molding. Important uses for TPU include manufacturing shoe soles, hoses, cable jacketing, coated fabrics such as conveyor belts, sewer liners and printing blankets, protective coatings, adhesives and melt spun elastic fibers.
TPUs are segmented polymers having soft segments and hard segments. This feature accounts for their excellent elastic properties. The soft segments are derived from the hydroxyl terminated polyether or polyester and the hard segments are derived from the isocyanate and the chain extender. The chain extender is typically one of a variety of glycols, such as 1,4-butane glycol.
U.S. Pat. No. 5,959,059 discloses a TPU made from a hydroxyl terminated polyether, a glycol chain extender, and a diisocyanate. This TPU is described as being useful for making fibers, golf ball cores, recreational wheels, and other uses.
In numerous applications, it would be desirable for the TPU to exhibit high tensile strength and a high elongation at break coupled with a melting point of less than about 175° C. In many of these applications, it would also be desirable for the TPU to be hydrophobic, to be capable of swelling in mineral oil, and to exhibit a low level of tensile set. However, soft TPUs having these combinations of physical characteristics have proven to be elusive. This is because TPUs made with hydrophobic polyols and traditional chain extenders, such as butane diol (BDO) and hexane diol (HDO), typically melt at exceptionally high temperatures that are not suitable in the applications being sought.
Plastic handles of various shapes and sizes are found on many household items. Such household items include toothbrushes, shaving razors, hairbrushes, pens, tools, kitchen appliances and kitchen utensils. These household items have a variety of functions, but in most cases, it is desirable for the user to grip the handle of these items firmly, so that it does not fall out of the user's hand. In other cases, such as with a knife, it is desirable for the handle to be gripped with even more firmness so that leverage can be applied.
Because the handles of household items are normally made with a hard plastic, the simplest tasks can become problematic for some people, such as the elderly and those suffering from arthritis in the joints of their hands. This problem is compounded in cases where the handle of the article, such as a toothbrush or shaving razor, come into contact with water making it more slippery. For instance, when a toothbrush or razor is wet, it is more difficult to grip and can slip out of the user's hands. Other items such as tools and kitchen utensils can have handles that are difficult to hold or uncomfortable to grip because of the hardness of the plastic material. For persons suffering from arthritis, carpal tunnel syndrome or other hand injuries or infirmities, using basic household objects can become difficult or even impossible.
Most people would prefer to hold objects with a softer handle that is more soothing to the touch and easier to grip. Accordingly, a need exists for a soft grip handles that can be grasped firmly and comfortably and which requires minimum strength and dexterity to grip and maneuver. There is, accordingly, a growing demand for a wide variety of articles that are soft and soothing to touch. It is, of course, also important for these articles to have the strength, durability, and rigidity needed in the applications where the article is used. This can be accomplished by overmolding a soft thermoplastic composition onto a hard thermoplastic substrate. However, there is a need for a soft thermoplastic elastomer composition that can be overmolded onto a hard thermoplastic resin substrate wherein the soft thermoplastic composition has lower hardness, good oil resistance and low compression set. There is currently a need for a thermoplastic composition that has superior feel and comfort as characterized by a lower modulus to that which is obtained by using syndiotactic polypropylene copolymer.